From a72caae21803b74e04e2afda5e035f149d4ea118 Mon Sep 17 00:00:00 2001 From: Jason Wang <jasowang@redhat.com> Date: Fri, 20 Jan 2012 16:17:08 +0800 Subject: [PATCH] virtio: correct the memory barrier in virtqueue_kick_prepare() Use virtio_mb() to make sure the available index to be exposed before checking the the avail event. Otherwise we may get stale value of avail event in guest and never kick the host after. Note: this fixes a bug introduced by ee7cd8981e15bcb365fc762afe3fc47b8242f630. Signed-off-by: Jason Wang <jasowang@redhat.com> Acked-by: Michael S. Tsirkin <mst@redhat.com> Signed-off-by: Rusty Russell <rusty@rustcorp.com.au> Cc: stable@kernel.org --- drivers/virtio/virtio_ring.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c index 78428a863b469..5aa43c3392a2a 100644 --- a/drivers/virtio/virtio_ring.c +++ b/drivers/virtio/virtio_ring.c @@ -308,9 +308,9 @@ bool virtqueue_kick_prepare(struct virtqueue *_vq) bool needs_kick; START_USE(vq); - /* Descriptors and available array need to be set before we expose the - * new available array entries. */ - virtio_wmb(vq); + /* We need to expose available array entries before checking avail + * event. */ + virtio_mb(vq); old = vq->vring.avail->idx - vq->num_added; new = vq->vring.avail->idx; -- GitLab